Mystery Plant! #764

John Nelson

Posted 3/18/24

By John Nelson

“Life’s a beach.” That’s what they say.
(Photo by John Nelson.)

This is a species of an oceanic, or “marine”, algae. It is indeed, one of the many species of “seaweeds”, a very non-technical term, but a term that is useful. Botanists consider the true seaweeds to be members of a taxonomic group called the “brown” algae, a group with hundreds of different species, including the giant kelps of many of the world’s cold-water coastlines. The brown algae are all oceanic, and are most common in cold, non-tropical waters, and their pigments often give them a dark, often brownish color. Although many are fairly large plants with rubbery, tough texture, others are smaller and fairly delicate. A number of the “browns” are attached to rocks or other substrates, whereas some float. Other than the brown algae, there are various other algal groups, including the green, golden, and red algal species. Any alga (the singular form of the word “algae”) floating in the surf, or for that matter any other plant washed up onto the sand, is likely to be referred to off-handedly as a “seaweed,” but this term really only refers to brown algae.

If you are at the beach this coming summer, you might run into some algae. Washed up on the beach, it is a common component of what we call beach “wrack,” or accumulated naturally occurring debris. Beach wrack is normally associated with the highest tide lines, where it provides habitat for a surprising number of animal species, and may assist with germination of some plants’ seeds. As it decomposes, nutrient recycling takes place. When amounts are sufficient, wrack is sometimes harvested as a source of compost or green manure. On the beaches of the Atlantic and Gulf Coasts, wrack commonly features the seaweed called “Sargasso weed”… and yes, much of it does originate from the part of the Atlantic Ocean called the Sargasso Sea. (Unfortunately these days, the wrack on many beaches contains more and more plastic and styrofoam—not to mention worse stuff, like oil—and becomes something of an eyesore.)

(Photo by John Nelson.)

But our Mystery Plant is an Asiatic species, naturally occurring along the coasts of Japan, Korea, and China. It commonly occurs in great abundance, forming towering forests beneath the waves. The fronds are also cultivated, especially in Japan, and especially around the island of Hokkaido, as an important food source. The fronds are rich in minerals, as you might expect from something that grows in the ocean. Moreover, the fronds are rich in iodine, which you need for a healthy thyroid gland. (But not too much of it.) When the fronds are dried, they obviously lose their water content, and can be easily marketed and stored. Cooking this alga requires a good bit of soaking. When sliced or chopped, it can be added to soups and stews, rendering delicately “oceanic” flavors, largely due to the presence of glutamic acid…and that is where the “umami” taste comes from. You might try some with your next dive into a sashimi platter.

[Answer: “Kombu,” Saccharina japonica]

John Nelson is the retired curator of the Herbarium at the University of South Carolina, in the Department of Biological Sciences. As a public service, the Herbarium offers free plant identifications. For more information, visit or email

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